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Many people are accustomed to thinking of the evolution of life in terms of a ladderlike progression, with a different animal on each rung. In the case of vertebrate evolution, they may envisage a fish on the bottom rung, a salamander on the next, then a lizard, a mouse, and finally, a human on top. But the ladder myth is misconceived and does not fit with evolution. Instead of resembling a ladder, the evolution of life is more similar to a branching bush, each branch of which represents a distinct lineage of organisms. Places where two or more branches diverge from a single point on the bush...

Many people are accustomed to thinking of the evolution of life in terms of a ladderlike progression, with a different animal on each rung. In the case of vertebrate evolution, they may envisage a fish on the bottom rung, a salamander on the next, then a lizard, a mouse, and finally, a human on top. But the ladder myth is misconceived and does not fit with evolution. Instead of resembling a ladder, the evolution of life is more similar to a branching bush, each branch of which represents a distinct lineage of organisms. Places where two or more branches diverge from a single point on the bush indicate that the lineages represented by the branches must have shared a common ancestor at a particular point in their history. In current evolutionary biology, the focus of investigation has shifted from finding transitional taxa to finding transitional features shared by closely related forms with common ancestry. The continuous reports on new discoveries of “transitional forms” show the large advances that have been made and are being made in the documentation of macroevolutionary steps of vertebrates since Darwin's time. These reports also show that purpose and plan are not characteristic of organic evolution. This chapter discusses studies of flatfish eyes, bat wings, turtle shells, and whale legs.